Start-stop systems configured to shut down an engine automatically when predetermined conditions are met are provided on many motor vehicles. Such systems reduce the time the engine is running during a journey performed by the vehicle and can thereby reduce fuel consumption and emissions over the journey.
For vehicles equipped with an automatic transmission, determining whether to shut down and/or restart the engine is often performed at least partially according to the operation of a brake system of the vehicle. For example, the start-stop system may be configured to shut down the engine of the vehicle when the brake pressure (or braking torque applied to the wheels) exceeds a threshold value and restart the engine when the brake pressure (or braking torque) drops below the threshold value or a further threshold value.
It is often desirable to select threshold values, or other conditions under which the engine is shut down and/or restarted, in order to maximize the reductions in fuel consumption and vehicle tailpipe emissions attained by the stop-start system. However, if the stop-start system shuts down and restarts the engine too frequently, it may become an annoyance to the driver and the driver may deactivate the stop-start system preventing any benefit to fuel consumption or vehicle emissions being achieved.
Driver preferences and driving styles, e.g. the braking behavior of drivers when bringing the vehicle to a stop, can vary significantly, and hence selecting the conditions under which the engine should be shut down and restarted by the stop-start system is challenging.